Pfeiffer is "absolutely tremendous," Rudd told Variety.
"And it was really cool to see Michelle Pfeiffer and Michael Douglas just on set. And I'd look over and go, 'Oh, my god. Legends,'" Rudd said. "So they're both really lovely people and it was a thrill to get to work with them."
Douglas reprises his Ant-Man role as cantankerous scientist Hank Pym, the original shrinking hero. Franchise newcomer Pfeiffer joins as Janet van Dyne, the original high-flying Wasp and long-lost mother of Pym's formerly estranged daughter, Hope van Dyne (Evangeline Lilly).
The role marks the three-time Oscar-nominated actress' return to the superhero movie genre since starring as Catwoman in 1992's Batman Returns.
"It had this great sense of humor about it and just this unusual tone," Pfeiffer said of 2015's Ant-Man, which convinced Pfeiffer to board its sequel. "This new script has the same thing. It's nicely written."
Hope suits up as the modern Wasp, joining Rudd's Scott Lang in action.
Pfeiffer is joined by Marvel Cinematic Universe newcomers Laurence Fishburne, who stars as Dr. Bill Foster, Randall Park as Agent Jimmy Woo, Walton Goggins as Sonny Burch, and Hannah John-Kamen, who portrays a villainness known as Ghost.
Michael Pena, David Dastmalchian, Tip 'T.I.' Harris, Judy Greer, and Abby Ryder Fortson reprise their Ant-Man roles.
Lilly said Ant-Man and the Wasp helps lead the Marvel Cinematic Universe towards a "colorful, more playful, heightened reality."
Part of the super-sequel will center around Ant-Man and Wasp's journey into the mysterious Quantum Realm, presumably to rescue the missing Janet:
"Those characters are experts in the quantum realm. In Ant-Man and the Wasp, they are trying everything in their power to safely enter the quantum realm and return back from it because they have evidence from the first film that Scott Lang was able to do that," Lilly explained.
She added, "If he can do it, why can't we? If we do succeed in Ant-Man and the Wasp, then that does open a whole entire new multi-verse to enter into and play around in. I'm not the story creator, so I can't tell you what they're going to do with that. But I definitely see the potential there."
Ant-Man director Peyton Reed directs from a script by Spider-Man: Homecoming's Chris McKenna & Erik Sommers and Highlander's Andrew Barrer & Gabriel Ferrari and Paul Rudd.
Ant-Man and the Wasp opens July 6.